The present invention generally relates to a temperature controller and more particularly, to a temperature control device arranged to control temperature of an object to be controlled, for example, to be close to a predetermined or set target value.
Conventionally, there has been proposed a temperature control device for controlling temperature of an object to be controlled, which is so arranged that, analog output signal corresponding to temperature of the object to be controlled is converted into a digital amount by an A/D converter so as to be applied to a digital operation or calculation unit, and a predetermined calculation is effected by the above digital operation unit based on said digital amount and a set target value, so that output control amount is produced by the result of the above calculation for being applied to the object to be controlled, thereby to control the temperature of said object. Although a thermo-couple, temperature measuring resistor or the like is employed as a temperature detecting means for the temperature control device of the above described type, the output of the thermo-couple or resistance value variation of the temperature measuring resistor as referred to above is very small, and therefore, if such outputs are to be directly applied to the A/D converter for processing as they are, an A/D converter having an extremely high resolving power is required. Accordingly, it has been a common practice to amplify the output of the thermo-couple, temperature measuring resistor or the like by an amplifier to a proper value for processing by the A/D converter, with such amplifier being normally constituted by one operational amplifier so as not to increase cost for the temperature control device on the whole. Therefore, in the known arrangement as described above, it is inevitable that the output of the amplifier contains ripple component of about several mV due to noises induced into input or power source voltage. Meanwhile, since the resolving power of the A/D converter is normally in the order of approximately 1 mV/bit, the output data of the A/D converter are undesirably altered only by the ripple component. Consequently, if the output data of such A/D converter are to be used for the control calculation, control is effected as if the temperature value were altered by the ripple component contained in the output data, even when the temperature is not actually varied, thus making it impossible to effect proper control as intended. Therefore, in some prior art temperature control devices, the A/D converter is employed in a double integral system for removing the undesirable ripple component. However, since the double integral system referred to above requires a comparatively long data measuring time, in the case where, for example, P.I.D. constant and other parameters, etc. are set in the form of analog values besides the analog output value from the temperature detecting means so that these various values are taken into the operation or calculation unit through conversion thereof into digital amount by one A/D converter, much more time is required for the processing, with a consequent reduction of processing speed of the temperature control device as a whole.